This project is designed to provide new insight into the mechanisms by which foreign DNA interacts with host chromosoml DNA. Specifically, we are studying the development of bacteriophage Mu in Escherichia coli. This virus resembles in many key features the animal DNA tumor viruses, DNA insertion sequences and DNA transposition elements. This year we will focus our efforts on the following areas: 1. Phage specified requirements for Mu DNA replication. 2. Host specified requirements for Mu DNA replication. 3. The fate, after induction, of plasmid DNA containing a Mu prophage.